An important factor in implementing and managing mobile telephone systems is the determination of quality of reception by mobile units of the signals broadcast by base transceiver stations (BTSs). This determination can be valuable in identifying the cause of, for example, high levels of interruptions to calls (dropped calls) in specific geographic areas. To this end, a "drive system" is used, comprising a small test system housed in a vehicle such as a car or van. The test system typically incorporates a "test mobile" handset, independent signal receiving and measurement equipment, a geographic location system (such as a global positioning system--GPS--receiver), and a mobile computer to coordinate the operation of these devices and record the results obtained.
One significant function typically desired in a drive system is the detection, measurement and identification of co-channel signals, i.e. signals occupying the same frequency band or channel as, and interfering with, the mobile telephone system signal intended to occupy that channel.
The conventional method of co-channel detection uses a directional antenna coupled to a receiver. While the vehicle is stationary the antenna is progressively rotated stepwise through a complete circle. At each directional setting the received signal strength is recorded and if need be demodulated to identify a possible interferer. All this information then has to be combined to form a complete picture of the reception characteristics at that location. This is a very complex and time-consuming process requiring a skilled technician for what is essentially a data collection process. Another drawback of this approach is that the separate measurements are temporally uncorrelated and so cannot represent the instantaneous received signal quality. To get around this, a multiple receiver/antenna setup can be used, but this is complex and costly.
It is an object of this invention to provide a method and apparatus for extraction of primary and co-channel signals which reduce the time required for the measurement to be made and which can be used with an omni-directional antenna.